In the art of producing iron-based ductile alloys that are castable, there are certain end-product applications that require the use of an iron-based alloy that yields enhanced high temperature strength end-products. Such end-products are used in a wide range of applications, one of those including “hot-side” engine parts. Typical of such parts are turbochargers, center housings, back plates, exhaust manifolds, and integrated turbo-manifold components that are used in the automotive and truck manufacturing industries. As with any product in the automotive industry, the market for such products is quite large and the number of products that are required to be produced is proportionately large.
Molybdenum and niobium (also somewhat archaically known as “columbium”) are alloying elements that are known in the art. Niobium is currently being used in the production of heat resistant stainless steels and aircraft engine parts. Molybdenum is also used in similar applications, but at a greater cost. Because niobium adjoins molybdenum in the periodic table, these elements have very similar atomic weights. The product of the present invention was intended to utilize niobium in such a way as to provide a high-silicon niobium ductile iron with acceptable heat-resistance properties with reduced cost in mind. That is, since large numbers of hot-side engine parts are used in the automotive industry, achieving sufficient high temperature strength while using niobium in place of molybdenum would contribute to reducing the cost of producing such parts. During testing, however, it was found that the alloy of the present invention not only met the requirement of achieving sufficient high temperature strength, but actually exceeded that requirement and ended up providing a unique high-silicon niobium ductile iron with enhanced heat-resistance characteristics, and with a probable saving of cost.
Another goal of the product of the present invention was to utilize niobium in such a high silicon casting alloy wherein existing industry-wide specifications and performance standards would be adhered to. More specifically, current high silicon molybdenum ductile alloys called out specific ranges for levels of certain elements to be used in the alloy and that the alloy would possess certain minimum performance characteristics following casting. This inventor was of the view that niobium could be used in a high silicon niobium alloy, at a savings of cost, while preserving the required performance characteristics that were dictated by the industry. Not only did this view prove to be true, but performance characteristics were found to be enhanced.
Still another goal of the product of the present invention was to utilize niobium in an ultra high silicon casting alloy wherein corrosion and oxidation resistance characteristics were improved. That is, where the addition of chromium in ultra high silicon molybdenum alloys results in improved oxidation and corrosion resistance, this inventor was also of the view that niobium could be used in an ultra high silicon and chromium ductile iron in place of molybdenum without any degradation of those characteristics. This view proved to be true and with performance actually being enhanced as well.